Mold clamping device for pressing machine

ABSTRACT

A mold clamping device for a pressing machine which bends a plate material inserted between upper and lower molds. The mold clamping device comprises a main frame ( 1 ) of integral structure, a holding ram ( 13 ) mounted on the upper half of the mainframe ( 1 ) and for supporting the upper mold ( 8 ) for vertical movement, a pair of arch-type thick springs ( 6 ) vertically mounted on the upper half of the main frame, and a crank mechanism ( 10 ) with which the upper end of each of the arch-type thick spring is connected through a crank pin ( 17 ). The crank mechanism creates a rotational force at a position near the dead center of the crank pins ( 17 ). This rotational force resiliently deforms the arch-type thick springs ( 6 ) which in turn create a resilient force for pressing the upper mold ( 8 ) against the lower mold ( 9 ). This provides an accurate and stable clamping force between the upper and lower molds.

TECHNICAL FIELD

The present invention relates to a mold clamping device for a pressingmachine in which a plate material is subjected to bending or otherworking between upper and lower mold sections clamped against eachother.

BACKGROUND ART

Various forms of pressing machines for bending plate materials areknown. Where a plate material is to be bent by a blade for upper andlower molds being clamped against each other, the blade tends to exert alarge force to the plate material, leading to a deviation therein. Ifthe upper mold is pressed against the lower mold by a linearly straightforce from a hydraulic cylinder or from a simple conversion of therotation of a motor, a very large power is required. The main body ofthe pressing machine supporting these power sources will be subjected tooverload.

The inventors have found the technical problems inherent in the proposedmold clamping device, improved it to overcome the problems and came upwith the present invention.

First of all, the technical problems raised by our previously proposedmold clamping device will be described in connection with FIG. 5.

The mold clamping device shown in FIG. 5 has a main frame 50 whichcomprises a lower frame portion 51 having a lower mold 53 and an upperframe portion 52 having an upper mold 54. The lower and upper frameportions 51, 52 are pivotally connected to each other at the rearwardends through a pivot shaft 55. The lower and upper frame portions 51, 52are also connected to each other at their forward ends through anarch-type thick spring 56. Thus, the structure thereof necessarilybecomes complicated. And yet, the arch-type thick spring 56 causes thewhole height of the mold clamping device to increase since the arch-typethick spring 56 must be curved rearwardly to an increased extent suchthat it will not interfere the plate bending action in the pressingmachine. In addition, the arch-type thick spring 56 is a bulky metalworking matter, for example, having a thickness of 15 cm and a width of20 cm in cross-section since it must provide a strong and instantaneousforce. This not only increases the manufacturing cost, but also requiresa huge driving energy for moving the upper frame portion together withthe arch-type thick spring. This additionally raises a poor response inpower transmission.

A crank mechanism 58 for driving the arch-type thick spring 56 isprovided on the upper frame portion at the top thereof. The upper end ofthe arch-type thick spring 56 is connected with a crank pin 60 in thecrank mechanism 58 while the bottom end thereof is supported by anotherpin 61.

In such an arrangement, the crank mechanism will provide an openingforce for elongating the arch-type thick spring. A closing spring forcefor depressing a holding ram 62 is created from a reactive forceassociated with the resilient opening deformation of the arch-type thickspring. However, the arch-type thick spring 56 highly restricts theamount of resilient deformation. It is thus difficult that the clampingforce is regulated into the desired level.

For such a reason, the length of the arch-type thick spring needs to beincreased. As a result, its point of action 60 will positioned upwardfrom the upper frame portion, so that a forward thrusting force P willact on the holding ram 62 in association with the structure ofopening/closing frame 1. This may destabilize the engagement between theupper and lower molds.

Even in the regulation of clamping force, the mold clamping devicehardly accommodates the change in the set height of the holding ram, forexample, due to mold exchange or corrective grinding since the amount ofresilient opening deformation in the arch-type thick spring is smaller,that is, the range of track using the clamping force in the crank pin 60is smaller.

Moreover, the upper mold must be replaced by another mold when it is tochange the plate bending process or the shape of the product. This isvery troublesome in operation. To facilitate such an operation, a shapedmold such as a rounded mold 21 may be placed on the upper mold 54. Toaccomplish this, the height of the holding ram 52 must greatly bechanged. However, this operation is very difficult since the holding ram62 must be moved up and down with the opening/closing motion of theupper frame portion 52, rather than the independent movement of theholding ram 62 itself. In addition, when any shaped mold is mounted onthe upper mold 54, a deviation tends to create in the engagement betweenthe upper and lower molds 54, 53 since the upper mold 54 mounted on theholding ram 62 will be moved up and down along a circular track R aboutthe pivot pin 55. To overcome such a deviation, the mold clamping devicemust be designed and regulated in an extremely delicate manner.

DISCLOSURE OF THE INVENTION

An object of the present invention is therefore to provide a moldclamping device for a plate bending pressing machine, which is of asimple structure with a low manufacturing cost, is superior in savingthe energy, provides an accurate and stable clamping operation and hasan improved operability.

To this end, the present invention provides a mold clamping devicecomprised in a plate bending pressing machine including a main framehaving an integral structure, upper and lower molds between which aplate material is inserted and the upper mold being pressed against thelower mold to bend the plate material, comprising:

a vertically movable holding ram for holding the upper mold;

at least a pair of left and right arch-type thick springs verticallymounted on an upper half of the main frame;

a crank mechanism being connected with each of upper portions of thearch-type thick springs through a crank pin and creating a rotationalforce at a position near a dead center on each of the crank pins,

wherein the rotational force of the crank mechanism compresses thearch-type thick springs to produce a resilient force which presses theupper mold against the lower mold.

In such an arrangement, the crank mechanism is actuated to lift theholding ram together with the arch-type thick springs for opening theupper mold. When the upper mold is opened, a plate material is insertedinto the machine. The crank mechanism is then re-actuated to lower theholding ram together with the arch-type thick springs for closing theupper mold. At this point, the arch-type thick springs are largelycompressed near the dead centers of the crank pins. Therefore, the platematerial may be clamped against the lower mold under an appropriateresilient force with flexibility but without being stiffened.Furthermore, since the holding ram is moved in the vertical direction,the upper mold may be accurately and stably engaged with the lower moldregardless of the height thereof.

The pressing machine of the present invention may comprise a C-shapedmain frame having an opening, upper and lower molds located within theopening, a blade drive located in the lower half of the main frame and ablade for bending the plate material clamped between the upper and lowermolds when driven. In such an arrangement, when the blade is to bend theplate material, the upper mold is clamped by the resilient force fromthe arch-type thick springs. Thus, a little deviation is created in theplate material. This provides stable bending with improved dimensionalprecision. The holding ram may include a bracket extending therefrom. Ifa displacement crank mechanism using the pins connecting the arch-typethick springs to the holding ram as crank pins is mounted on thebracket, the upper mold can be mounted and used when the holding ram islifted by the displacement crank mechanism. The holding ram is slidablyand vertically held on guide rails on the main frame through guideblocks.

According to the present invention, the upper portion of the integralmain frame structure can include relatively small arch-type thicksprings. Thus, the present invention may provide a simple andinexpensive structure with less energy. Since the crank mechanismvertically drives the upper mold holding ram through the arch-type thicksprings to compress them, the compressed arch-type thick springscreating the resilient force for clamping the molds, the clampingprocess can be quickly carried out with accuracy and stability. Inaddition, the displacement crank mechanism using the pins connecting thearch-type thick springs to the holding ram as crank pins can provideadvantages in that the machine can properly accommodate changes andmodifications of the mold and improve the operability. In theaforementioned structure of the crank mechanism, the displacement crankmechanism located on the bottom of the arch-type thick springs may beused for clamping the upper mold while the crank mechanism on the topend thereof may be used to displace the upper mold for mounting a shapedmold thereon.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a plate bending pressing machine according onepreferred embodiment of the present invention;

FIG. 2 is an enlarged side view of the main parts in the mold clampingdevice of the plate bending pressing machine;

FIG. 3 is a front view of the plate bending pressing machine;

FIG. 4 is an enlarged side view of the primary parts of the pressingmachine when a shaped mold is mounted therein; and

FIG. 5 is a side view of a pressing machine according to the prior art.

BEST MODES FOR CARRYING OUT THE INVENTION

The present invention will be described in connection with the work ofplate material as shown in the accompanying drawings.

Referring to FIG. 1, a plate bending pressing machine comprises a mainframe 1 having an integral structure including side plates 3. The mainframe 1 also includes an intermediate opening 5 into which a platematerial W is to be inserted. The upper half of the main frame 1 abovethe opening 5 includes a mold clamping device A including a pair of leftand right arch-type thick springs 6. The lower half of the main frame 1below the opening 5 includes a drive B for a blade 7. When an upper mold8 clamps the plate material W against a lower mold 9 through the moldclamping device A, the plate material W is bent into a predeterminedshape by the blade 7. The blade 7 has vertically bifurcatedconfiguration so that the plate material W can be bent easily in bothforward and backward directions.

The mold clamping device A includes a crank mechanism 10 which includesa crank shaft 11 rotatably mounted on the upper end of the main frame 1at an upper position of the opening 5. The mold clamping device A alsoincludes a bracket 15 located below the crank shaft 11 and laterallyextending from a holding ram 13 and a pair of left and right arch-typethick springs 6 each of which connects between a crank pin 17 and eachof the brackets 15. The lower end of each of the arch-type thick springs6 is connected with the corresponding bracket 15 through a pin 18. Theholding ram 13 is supported for vertical movement, by so-called LM guiderails 20 on the main frame 1 through guide blocks 22 on the holding ram13.

The trajectory of movement in the crank pins 17 is as shown byone-dot-chain line. A servomotor 19 having a reduction gear rotatablydrives the crank pins 17 to move the arch-type thick springs 6 in thevertical direction. Thus, the holding ram 13 is vertically moved to openor close the upper mold 8. When the upper mold 8 is opened, the platematerial W is inserted into the opening 5. The crank pins 17 are thenrotated in the downward direction to close the upper mold 8. At aposition near the bottom dead center, an additional pressure is createdto compress the arch-type thick springs 6 so as to produce a resilient,stable and strong force by which the upper mold 8 clamps the platematerial W against the lower mold 9.

At this point, it is assumed that the holding ram 13 has height L. Inthis embodiment, furthermore, a displacement crank mechanism 23 ismounted on each of the brackets 15 and moves the holding ram 13 to anupward position M for mounting a shaped mold 21 on the underside of theupper mold 8. Each of the displacement crank mechanisms 23 includes aservomotor 25 with a reduction gear for driving it. Each of thedisplacement crank mechanisms 23 also includes a crank shaft 27rotatably driven by the servomotor 25. The connection pin 18 in each ofthe arch-type thick springs 6 functions as a crank pin in thecorresponding displacement crank mechanism 23. As the crank pins 18 areat or near its top dead center, the shaped mold 21 is used.

Automatic mounting devices 29 are used to mount the shaped mold 21. Eachof the automatic mounting device 29 comprises a vertically movableslider 31, an arm 33 for mounting the shaped mold 21 and an air cylinder35 for driving the arm 33 invertedly. The shaped mold 21 has a roundedworking face which cooperates with the blade 7 to bend the platematerial W into the desired rounded form. Since the shaped mold 21 ismoved in the vertical direction without outwardly deforming the holdingram 13, the shaped mold 21 can uniformly and accurately be pressurizedagainst the lower mold 9 by simply parallel working the top and bottomfaces of the shaped mold 21.

The drive B for the blade 7 is in the form of a linkage comprising adrive link 37 extending substantially in X-axis direction and anotherdrive link 39 extending in Y-axis direction and coupled with the drivelink 37. Each of the links 37 and 39 is driven by any suitable crankmechanism. Reference numeral 40 denotes an automatic control box.

INDUSTRIAL APPLICABILITY

As described, the mold clamping device in the pressing machine accordingto the present invention is particularly effective for various bendingfields such as forward bending and backward bending. Nevertheless, themold clamping device can similarly be used to perform highly accuratebending directly using the upper and lower molds as for example when aV-shaped bending is to be carried out by using a lower mold having aV-shaped groove and an upper mold of V-shaped wedge configuration.

What is claimed is:
 1. A bending pressing machine, comprising: a mainframe; a lower mold supported on the main frame; an upper mold forpressing a plate material inserted between the lower and upper molds; atleast one arch-type thick spring being mounted on an upper half of themain frame and extending in a vertical direction; a blade driving devicemounted on a lower half of the main frame; a blade driven by the bladedriving device to bend the plate material pressed between the lower andupper molds; a first crank mechanism being connected with an upperportion of the at least one arch-type thick spring through a first crankpin; a holding ram for supporting the upper mold and being mounted onthe main frame for vertical movement; a second crank mechanism beingconnected with a lower portion of the at least one arch-type thickspring through a second crank pin; and a bracket extending from theholding ram and connected with the lower portion of the at least onearch-type thick spring through the second crank pin, wherein the uppermold comprises a first upper mold moved up and down by the holding ramand a second upper mold disposed on an underside of the first uppermold, the plate material being inserted between the second upper moldand the lower mold.
 2. The bending pressing machine as defined in claim1, wherein the main frame is configured in a C-shape and includes afront opening into which the plate material is to be inserted andwherein the upper and lower molds are positioned within the opening. 3.The bending pressing machine as defined in claim 1, wherein a pair ofthe arch-type thick springs are mounted on the upper half of the mainframe.
 4. The bending pressing machine as defined in claim 1, furthercomprising: guide rails on the main frame; and guide blocks beingslidably mounted on the guide rails and supporting the holding ram. 5.The bending pressing machine as defined in claim 1, wherein the secondupper mold is disposed between the first upper mold and the lower moldwhen the first crank mechanism moves the lower portion of the at leastone arch-type thick spring in an upward direction, and wherein the platematerial is clamped between the lower mold and the second upper moldwhen the second crank mechanism moves the lower portion of the at leastone arch-type thick spring in a downward direction at a rotationalposition of the second crank mechanism near a dead center of the secondcrank pin.
 6. The bending pressing machine as defined in claim 1,wherein the blade comprises blade sections for bending backwards andforwards.
 7. The bending pressing machine as defined in claim 1, whereinthe second upper mold is disposed between the first upper mold and thelower mold when the second crank mechanism moves the lower portion ofthe at least one arch-type thick spring in an upward direction, andwherein the plate material is clamped between the lower mold and thesecond upper mold when the first crank mechanism moves the lower portionof the at least one arch-type thick spring in a downward direction at arotational position of the first crank mechanism near a dead center ofthe first crank pin.